1. Field of the Invention
The invention relates to a binder, methods for binding bulk materials and loose formations with this binder and bound products produced therewith.
2. Discussion of Background Information
Binders for binding bulk materials and loose formations are known. Thus, for example, DE-A-102004004615, EP-A-06706316, WO 2007/121972 and WO 2007/121975 describe systems which are used for consolidating bulk materials or loose formations. As a rule, a procedure is adopted in which a reactive soluble system is infiltrated into a bulk material or loose formation and is solidified via a reaction. Various materials are used for this purpose, for example organic monomers, hydrolysable and condensed alkoxides which are activated via sol-gel reactions, or mixtures of the two.
What is of decisive importance is that the solidification or curing reaction starts only when the infiltration process is complete. Otherwise, there is the danger that the binder will block, for example, feed lines or will solidify on the surface of the bulk material to be infiltrated and will not penetrate into the bulk material. The setting behaviour of the binder must therefore be adjusted so that solidification begins reliably only when the infiltration is complete or when a part of the binder is washed out or blown out again by a further step in order to maintain porosity.
In order to achieve this, the kinetics of the setting process must be well known and must be capable of being established in an exactly reproducible manner. For example, free radical polymerization mechanisms which have a known initial period are suitable for this purpose. It has been found, for example, that thermally initiatable peroxides are suitable as free radical formers. Pure sol-gel systems are also suitable but they show a strong dependence on external boundary parameters, such as, for example, pH and water content. These are so-called “living systems” whose stability declines with time so that they are frequently not particularly suitable for specific technical purposes.
The abovementioned prior art describes systems which were intended for the consolidation of bulk materials or loose formations. Mixed systems comprising sol-gel compositions, organic monomers or oligomers having reactive double bonds and initiators based on peroxides are described. The peroxides are chosen so that, after reaching the initiation temperature, a certain time elapses before a significant effect is found in respect of an increased viscosity of the system. The initiation temperature is the temperature at which the decomposition rate of the peroxides is sufficient for starting a polymerization chain reaction.
In this way, for example, a monomer solution which is provided with a corresponding initiator can be infiltrated into a bulk material which is kept at a specified temperature, and the consolidation can be induced after a specified time via the initial period peculiar to the initiator. Exact tailoring of the predetermined temperature of the bulk material, the decomposition temperature of the initiator and a knowledge of the enthalpy of reaction is required in order to avoid so-called “run-away” of the reaction and, as a result of this, consolidation at too early a stage.
However, the abovementioned prior art does not discuss the effect of finely divided components on the course of the chain or solidification reaction or take this into account. Thus, in our own investigations, it was found that finely divided components, e.g. phyllosilicates or milled ceramic components or oxides (clay minerals, Al2O3, ZrO2, Fe2O3, earthenware or stoneware), lead to early initiation of free radical formation from peroxide initiators, presumably due to catalytic effects at corners and edges of very fine particles present in the system. Thus, the addition of very fine oxide particles, such as fine clay minerals and finely milled ceramic particles, reduced the “open” time (time to gel formation or an increase in viscosity by several powers of ten) from about 4 hours to about 1 hour. Since no statement can be made about the presence, the type, the amount and the activity of such particles, particularly in natural formations which are to be bound, the presence of such particles in the systems to be bound is also an obstacle to the use of such binder systems in practice.
Systems described in WO 2007/121972 and WO 2007/121975 are scarcely suitable in practice owing to the abovementioned problems.
It was therefore the object to provide a binder which is suitable for binding bulk materials of all kinds or geological formations and ensures that it is not impaired in its mode of action by active surfaces of very fine particles, in particular with regard to the “open” time explained above. In particular, this should be achieved for binders with free radical initiators, such as peroxide initiators, on use of the above-described principle of free radical polymerization with a delayed action after the infiltration of bulk materials.
In addition, with the simultaneous use of polycondensable alkoxides, in particular with the use or concomitant use of silanes, the influence of the pH on the condensation process is considerable. This results in the danger that an influence, for example relating to the bulk material or formation, on the pH likewise has an influence on the open time. This too is not discussed in the above prior art.
It has now surprisingly been found that, by buffering reaction mixtures comprising precondensed sol-gel systems and organic binder components, such as monomers, with a buffer solution, in particular comprising an organic acid and a conjugated base, such as an acetic acid/acetate buffer, no influence at all of very fine particles on the properties of the binder is observable.